I had to rebuild my front driveline. I asked a machine shop if he could make a bigger one for me. He said in his experience that for a larger diameter shaft on a suspension lift of 4in on the CJ7 that the larger shaft is going to hit the cross member at full flex. He said I could put in a dual yoke to fix the problem but they tend to wear out faster. Any thoughts suggestions?
1981 CJ7 with a 4in Rough Country lift

It will be close as it is with a 4" lift so he's got a point. Don't beef up the u-joints though, you want them to be the weak link in any drivetrain. They are the easiest and cheapest to fix, should things be over stressed. And the 30 isn't a brute to begin with.

I also have a re-tubed rear driveline in the front. I have a relatively short transmission (T-177), and have 1/2" clearance at full droop, 2 1/2" lift, though. All sorts of factors make a difference, motor mounts, transmission mount are all new on mine.

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There are some things you will learn while holding a cat by the tail that can be learned no other way...